“In the 2007 [Olympic marathon] trials I could not walk or stand because of a stress fracture,” Keflezighi says. Stress fractures, small cracks in a weight-bearing bone of the body, are tricky because runners usually have high tolerance for pain due to the release of endorphins. However, if you feel more pain as a run progresses and a sore type of pain after a run,, you may have the injury. Swelling is also a sign. Surgery may be required. Other treatments are suing a walking boot, brace, or crutches.